It's a little strange for it to cause problems with an otherwise healthy young person. OTOH, my mother, 78, does take antibiotics for a few days before and after a dental visit. This is due to a combination of her age and the blood thinning drugs she takes.
It's possible that he had an undetected disorder that was triggered by the infection.
This whole controversy would been prevented if the medical staff had acted with the slight bit of sensitivity. Losing a child would be a tremendous shock to any parent, particularly given the way he died.